1. Field of the Invention
The present invention relates to an actuator and more particularly to a structure of an integral type differential actuator comprising two unit actuators and a differential mechanism, capable of attaining a wide speed range from zero to a desired speed. The actuator of the present invention is advantageously applicable as a drive source for an arm of an industrial robot.
2. Description of the Prior Art
One of the generally known differential actuators is shown in FIG. 8, in which the reference numeral 61 denotes an electric motor; numeral 62 denotes a coupling attached to a shaft end of the motor 61; numeral 63 denotes an input shaft connected to the coupling 62; numeral 64 denotes an input-side gear mounted on a distal end of the input shaft 63; and numeral 65 denotes a differential gear attached to a box 66 through a bearing, the rotation of the box 66 being controlled by a speed governor 67 which is in contact with a contact member 66a. Numeral 68 denotes a bearing which supports the box rotatably, and numeral 69 denotes an output-side gear mounted on a driven end of an output shaft 70 and connected to the differential gear 65.
In speed control, for example in the case of a Leonard thyristor control, a DC motor is used and the speed is changed by controlling the armature voltage or the field current. Alternatively, speed can be controlled by the actuator of FIG. 8 wherein, the input-side gear 64 is rotated by the motor 61 connected to the input shaft 63 through the coupling 62 as shown in the figure to thereby rotate the differential gear 65 connected to the gear 64. At this time, the differential gear 65 not only rotates on its own axis but also rotates together with the box 66 because it is connected to the box. Therefore, the speed of the box 66 can be controlled by changing the peripheral speed of the speed governor 67 and consequently the rotating speed of the output shaft 70 is controlled through the output-side gear 69.
Since the conventional actuator as a speed change mechanism is constructed as above, the speed control range is practically not larger than 1:3000 and problems such as torque ripple at low speeds and backlash have been involved therein.